In obstetrics, fetal heart rate monitoring has been the standard for intrapartum assessment of fetal well being. However, oximetry (oxygen saturation monitoring) can markedly improve medical care in many fields, including anesthesiology, intensive care, and newborn intensive care, because oximetry can allow direct assessment of both fetal oxygen status and fetal tissue perfusion. Unfortunately, fetal oxygen saturation monitoring has proven to present several technical obstacles. Pulse oximetry, a subclass of the general field of oximetry, uses changes in arterial blood volume through a heart beat cycle to internally calibrate oxygen saturation measurements.